1. Field of the Invention
This invention relates to a master information carrier for magnetic transfer carrying thereon an irregularity pattern representing information to be transferred to a magnetic recording medium.
2. Description of the Related Art
This invention is applied to magnetic transfer in which a master information carrier (patterned master) having thereon an irregularity pattern (pattern of protruding portions) representing information (e.g., a servo signal) to be transferred and a magnetic layer provided at least on the surface of the irregularity pattern is brought into close contact with a magnetic recording medium (a slave medium), and a transfer magnetic field is applied to the slave medium and the master information carrier in close contact with each other, thereby magnetically transferring a magnetization pattern representing the information carried by the master information carrier from the master information carrier to the slave medium.
A master information carrier comprising a substrate provided on its surface with an irregularity pattern representing information to be transferred and a thin magnetic layer formed on the surface of the irregularity pattern is disclosed, for instance, in U.S. Patent Laid-Open No. 20010028964.
Basic steps of the magnetic transfer will be described with reference to FIGS. 2A to 2C, hereinbelow. In FIGS. 2A to 2C, the magnetic transfer by in-plane recording is shown. A slave medium 2 having a magnetic layer to which information is magnetically transferred and a master information carrier 3 comprising, as shown in FIG. 2B, a substrate 31 provided on its surface with an irregularity pattern representing the information to be transferred and a magnetic layer 32 formed on the surface of the irregularity pattern are first prepared. An initial magnetostatic field Hin is first applied to the slave medium 2 in one direction parallel to the recording tracks thereof, thereby magnetizing the slave medium 2 in an initial magnetization (DC erasure) as shown in FIG. 2A. Thereafter, the magnetic layer 32 on the upper surface of the protruding portions of the irregularity pattern on the surface of the substrate 31 of the master information carrier 3 is brought into a close contact with the recording surface of the slave medium 2. In this state, a transfer magnetic field Hdu is applied in the direction opposite to the initial magnetic field Hin as shown in FIG. 2B, thereby magnetically transferring the information on the master information carrier 3 to the slave medium 2. Since the transfer magnetic field Hdu is absorbed in the magnetic layer 32 on the upper surface of the protruding portions of the irregularity pattern on the surface of the master information carrier 3 and accordingly, the magnetic field is not reversed at portions opposed to the protruding portions and is reversed at portions not opposed to the protruding portions. As a result, magnetization pattern corresponding to the irregularity pattern on the master information carrier 3 is transferred to the tracks of the slave medium 2 as shown in FIG. 2C. Information can be magnetically transferred to a slave medium also in a perpendicular recording system by the use of a master information carrier having substantially the same irregularity pattern of a magnetic layer.
In such patterned magnetic transfer, a high quality signal can be transferred to a slave medium by designing the master information carrier so that the magnetic fluxes are efficiently converged between the protruding portions of the irregularity pattern of the master information carrier.
Conventionally, the master information carrier has been produced so that the thickness of the magnetic layer formed on the irregularity pattern is smaller than the depth of the recessed portions on the basis of the idea that absorption of magnetic fluxes by the magnetic layer on the protruding portions of the irregularity pattern of the master information carrier is increased by making the magnetic layer on the protruding portions structurally independent from that on the recessed portions of the irregularity pattern. That is, conventionally the distance between the lower side of the magnetic layer on the protruding portions and the upper side of the magnetic layer on the recessed portions is large so that the former and the latter are isolated from each other. This has contributed to increase in reproduction output in reading the magnetization pattern transferred to the slave medium but causes sub-peaks (noise) to appear in the reproduction waveform. As a result, desired information cannot be recorded on the slave medium.
That is, when the magnetization pattern is magnetically transferred to a slave medium from such a master information carrier, though peak outputs are generated in the waveform of the signal reproduced from the slave medium corresponding to opposite ends of the magnetic layer on the protruding portions of the master information carrier, sub-peaks can appear forward or rearward of the peak output as noise and the sub-peak waveform can be read as representing the information.
It is preferred from the viewpoint of magnetic transfer properties that the magnetic layer is provided only on the protruding portions and not provided on the recessed portions. However it is difficult to provide the magnetic layer only on the protruding portions and such a master information carrier is disadvantageous in cost.